Power amplifiers (PAs) are used to amplify an input signal prior to providing an amplified output signal to a load. For instance, PAs are used for RF applications, where the PAs are typically coupled to an antenna arrangement. In other cases, PAs are for example used for delivering the amplified signal to a speaker.
In delivering power from the PA to a load coupled thereto, an impedance match between the PA, coupling circuit and the load is important in order to facilitate maximum power transfer therebetween. Transferring less then the maximum power results in unnecessary energy consumption by the PA, since this extra energy not transferred is lost. For instance, when antennas are coupled to PAs, then proper impedance matching is preferable because maximum power transfer occurs therebetween.
A Voltage Standing Wave Ratio (VSWR) is used for antenna systems to measure the coupling efficiency between the PA and the antenna arrangement. Typically, most antennas are not directly connected to the PAs. The antenna is usually located some distance from the transmitter, in the form of a PA, and requires a feedline, in the form of a coupling circuit, to transfer power therebetween. If the feedline has no loss, and is impedance matched to both the PA output impedance and the antenna input impedance, then maximum power is delivered to the antenna. In this case the VSWR is 1:1 and the voltage and current are constant over the whole length of the feedline. Any deviation from this situation causes a “standing wave” of voltage and current to exist on the feedline therebetween. This standing wave results in energy used for driving the PA to be wasted and thus leads to system inefficiencies.
Measuring of the VSWR is typically performed using voltage detectors disposed within the PA. Unfortunately, voltage detectors do not take into account load mismatching between the power amplifier and a device coupled thereto. Therefore, coupling values obtained using the voltage detectors may not be representative of actual coupling therebetween. As a result, reliable values for the VSWR may not be provided.
A need therefore exists for a way of measuring power coupling between a PA and a load that uses other than voltage detectors. It is therefore an object of the invention to provide a method of measuring power coupling between a circuit for emitting an electrical signal and a load coupled thereto by using induced current flow.